The sensing of nutrient levels and allocation to use versus storage of nutrients have fundamental importance to all animals and profoundly affect many life history traits, such as longevity, fecundity, and starvation resistance. Although the metabolic, neuromodulatory, and homeostasis genes thought to control this allocation are highly conserved across animals and center on the insulin-signaling pathway, the sensing mechanisms of the insulin response are not well studied. This project uses a combination of gene functional and population genetic approaches in Drosophila to address the hypotheses that (1) nutrient sensing mechanisms are conserved in animals and (2) that naturally occurring genetic variation in energy sensing genes provides a way by which natural selection can adaptively alter energy-stats to change nutrient allocation strategies. Aim 1 will use gene expression manipulations to initially assess the distribution of nutrient sensing ability among a selected group of metabolic and dopamine pathway genes, many of which are associated with human life history traits or disorders. For those loci in Aim 1 exhibiting positive effects we will determine in Aim 2 if gene knockouts have direct effects through fundamental flux control or indirect effects through modifying sensing state in neurosecretory cells. This will be accomplished by cell ablation of the neurosecretory cells. Aim 3 will examine genetic interactions of the loci of interest with known homeostatic signaling pathways, most notably the insulin pathway. If ablation of neurosecretory cells abolishes gene-specific effects then we would also expect significant changes in these effects in the presence of partial knockout of insulin-like peptides and adipokinetic hormone, which are secreted from those cells, as well as genotype-specific interactions with mutations in the neuropeptide receptors. Aim 4 will examine the population and expression variation of prospective nutrient sensor genes to determine which of these are targets of selection on fundamental life history strategies that are geographically variable in Drosophila. Mechanisms of energy signaling are a critical question in metabolic biology with significant ramifications for human health. This project will evaluate in Drosophila hypotheses on mechanisms believed operating in mammals and therefore conserved. In doing this, it will help establish these general features of energy sensing, and the potential for use of the Drosophila model to better understand metabolic disorders in humans.